An inertial navigation system (INS) with a low-performance inertial measurement unit (IMU), which is only aided with relative aiding sensors, is susceptible to filter inconsistency for heading estimates. Relative aiding sensors are aiding sources that do not provide absolute navigation information. In a navigation system that uses measurements from a low-performance IMU, the heading error can grow quickly without absolute aiding sensors. The development of heading inconsistency is likely to occur when the navigation system does not have the sensing necessary to observe absolute heading.
An INS can generally observe absolute heading if either a high-quality IMU or an absolute aiding sensor are present. Absolute heading observability is available from a high-quality IMU, which provides the INS with gyrocompassing ability when the velocity of the INS with respect to Earth is known; e.g., this condition commonly occurs when the INS is stationary with respect to Earth, a zero-velocity condition. Alternately, absolute heading observability is available when absolute sensing (e.g., GPS position or GPS velocity) is coupled with appropriate trajectory kinematics, i.e. acceleration of the INS with respect to Earth, or when a calibrated magnetometer is coupled with sufficient horizontal magnitude of the earth's magnetic field.
A number of applications typically use a low-performance IMU which is only aided with relative aiding sensors. For example, simultaneous localization and mapping (SLAM) in robotic systems and personal navigation systems in denied environments, which have no access to GPS input, are two applications that are susceptible to heading inconsistency.